Mazda 1300 - Chasis Rail Rust Repair

While engine was out, I took the oportunity to investigate the problem for all 1300's, chasis rail rust. The factory external voltage regular is a piece of junk and fails and causes battery overcharging. The lack of any battery box and a chasis rail that has a U shape to hold acid makes for a very rust rail. The top section was replaced 5 years before by first owner, but the bottom half far gone enough I could stick screwdrivers through